Show Assigned/Authored/All filter for dashboard issues and mr pages

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Add tests to Dashboard#merge_requests filter

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Tests for Dashboard#issues filter

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'feature/all_merge_requets' of /home/git/repositories/gitlab/gitlabhq